Measurements and/or estimates of exhaust pressure of an exhaust flow flowing through an exhaust passage of an internal combustion engine may be used as inputs in various vehicle control strategies in order to control engine operation. In one example, engines may include a dedicated, standalone pressure sensor positioned in an exhaust passage of the engine, upstream of a catalyst, to measure exhaust pressure. As such, accurate exhaust pressure measurements may be important for controlling operation of various vehicle control strategies.
Additionally, excessive exhaust pressures in an engine may result in increased pumping losses and fuel consumption. Flow restrictions in the exhaust, such as particulate filters, may exacerbate exhaust pressure spikes. For example, a particulate filter restricts exhaust gas flow and increases exhaust pressure as it becomes more loaded with soot. Particulate filters may be regenerated periodically to purge accumulated particulate matter. However, such regeneration events may come with at the expense of fuel consumption. As a result, accurate exhaust pressure estimates are needed to determine the loading state of the particulate filter and schedule regeneration of the particulate filter at optimal times that minimize fuel consumption. Further, accurate estimates of the exhaust pressure are important to prevent and/or minimize exhaust pressure spikes.
However, some engines may not include an exhaust pressure sensor. Dedicated exhaust pressure sensors may increase engine system costs and engine system control complexity. In such examples, the exhaust pressure may be modeled based on alternate engine operating conditions such as intake mass airflow, and/or sensor measurements.
However, the inventors herein have recognized that these exhaust pressure models may have errors that may cascade into additional models that use the modeled exhaust pressure. For example, approaches aimed at measuring exhaust pressure based on intake mass airflow may have reduced accuracy as they do not account for the effects of exhaust restrictions such as particulate filters of the exhaust pressure. Additionally, certain models may be bounded by a window in which exhaust pressure may only be modeled under certain engine operating conditions. As a result, engine control based on exhaust pressure estimates during operation outside of the window may have reduced accuracy.
In one example, the issues described above may be addressed by a method for monitoring periodic waveform outputs from an exhaust air/fuel ratio (AFR) sensor during closed loop fuel control, estimating an exhaust pressure based on one or more of a standard deviation and average frequency of cycles of the periodic waveform outputs, and adjusting at least one engine operating parameter based on the estimated exhaust pressure. In this way, an existing engine sensor (e.g., an exhaust AFR sensor) may be used to more accurately estimate engine exhaust pressure, thereby increasing an accuracy of engine control based on exhaust pressure estimates.
As one example, the AFR sensor may comprise an exhaust gas oxygen sensor and may be configured to measure a partial pressure of oxygen in exhaust gas. A controller may adjust an amount of fuel injected into one or more engine cylinders based on the outputs received from the AFR sensor. Thus, fuel injection may be feedback controlled based on the AFR sensor. However, since the oxygen sensor measures the partial pressure of oxygen in the sampled exhaust gas, the amount of oxygen measured by the sensor increases for increases in the exhaust pressure and therefore exhaust gas density. As such, fluctuations in the outputs of the AFR sensor may be used to infer changes in the exhaust gas pressure. In particular, the AFR sensor output may comprise a periodic waveform signal resulting from continuous oscillation between leaner than stoichiometry and richer than stoichiometry fuel injection commands. One or more of the frequency, amplitude and/or standard deviation of the periodic waveform signal of the AFR sensor may fluctuate in proportion to changes in the exhaust pressure. Thus, changes in the characteristics of the waveform output of the AFR sensor may be indicative of exhaust pressure changes. A controller may then adjust engine operation based on the determined change in exhaust pressure.
In another representation, a method comprises monitoring periodic waveform outputs of a fuel controller during closed loop fuel control, estimating an exhaust pressure based on the waveform outputs of the controller, and adjusting at least one engine operating parameter based on the estimated exhaust pressure.
In yet a further representation, an engine system comprises an exhaust oxygen sensor, one or more fuel injectors, and a controller with computer readable instructions stored in non-transitory memory for: determining a commanded amount of fuel to be injected by the one or more fuel injectors based on outputs from the exhaust oxygen sensor, adjusting the one or more fuel injectors to inject the commanded amount of fuel, and estimating an exhaust pressure based on one or more of the outputs from the exhaust oxygen sensor and changes in the commanded amount of fuel over a duration.
In this way, more accurate estimates of the exhaust pressure may be obtained that account for flow restrictions in the exhaust. As a result, engine control based on exhaust pressure estimates may be improved. Further, the cost of the engine system may be reduced by using utilizing an existing engine sensor to estimate exhaust pressure instead of a dedicated pressure sensor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.